Variable electrical resistance device



Jan. 24,, 1967 Q BELLAR I VARIABLE ELECTRICAL RESISTANCE DEVICE Filed Oct. 24, 1965 2 Sheets- Sheet .1

[Wen/r63 05cm? 351.49g.

Jan. 24, 1967- O, B AR 3,300,747

VARIABLE ELECTRICAL RESISTANCE DEVICE Filed Oct. 24, 1965 2 Sheets- Sheet z jA/vauroz scmQ LL/QP,

United States Patent C) 3,300,747 VARIABLE ELECTRICAL RESISTANCE DEVICE Oscar Bellar, Alhambra, Calih, assignor of thirty-five percent to Terence Dalby, Alhambra, Calif. Filed Oct. 24, 1965, Ser. No. 504,901 9 Claims. ((11. 338-143) This invention relates to variable electrical resistance devices which may be either rheostats or potentiometers and particularly to a form thereof capable of being manufactured in miniature and sub-miniature sizes.

The principal object of the invention is to provide a device for manually varying resistance imposed on an electrical current, said device including a helically wound resistance assembly and a shorting brush element rotatable thereon and in which the helical arrangement of the conductors of the resistance assembly additionally serve as threads whereby rotation of the brush element will cause it to move along the helix of the resistance unit.

A further object of the invention is to provide a variable resistance means of the above character in which the shorting brush element includes means yieldingly engaging the helically wound resistance assembly to permit non-rotative bodily axial movement of the brush element along the resistance assembly in addition to the rotative movement above referred to.

With the foregoing objects in view together with such additional objects and advantages as may subsequently appear, the invention resides in the parts and in the construction, combination and arrangement of parts described, by Way of example, in the following specification of certain presently preferred embodiments of the invention, reference being had to the accompanying drawings which form a part of said specification and in which drawings:

FIG. 1 is a side elevational view of a typical actual size first embodiment of the invention mounted on a panel element such as a printed circuit board,

FIG. 2 is an enlarged side elevation similar to FIG. 1 with a portion of the adjusting brush means broken away,

FIG. 3 is a further enlarged view similar to FIG. 1 with still other portions broken away,

FIG. 4 is an end elevation as viewed from the top end of FIG. 3,

FIGS. 5, 6, 7 and 8 are sectional views taken on the lines 5-5, 66, 77 and 8-8 of FIG. 3,

FIG. 9 is a perspective view of an alternative form of brush spring component,

FIG. 10 is a circuit diagram of a representative form of winding arrangement for the embodiment shown in the preceding figures,

FIG. 11 is a view generally similar to the first embodiment but showing the device connected to the printed side of a printed circuit board,

FIG. 12 is a transverse sectional view taken on the line 12-12 of FIG. 11,

FIG. 13 is a side elevational view generally similar to the devices shown in the preceding figures but showing the resistance assembly and brush component mounted on the reverse side of a printed circuit board and the brush component adjusted by a cover sleeve component,

FIGS. 14 and 15 are enlarged scale, transverse, sectional views taken on the lines 1414 and 1515 of FIG. 13,

FIGURE 14:: is a transverse sectional view similar to FIGURE 15 but incorporating thebrush of FIGURE 9,

FIG. 16 is a side elevational view of a resistance assembly and brush component operated on the same principle as the previous embodiments and adapted to be incorporated in the various types of mountings,

FIGS. 17, 18 and 19 are, respectively, side elevational, partly in section, bottom plan, and end elevational views 3,300,747 Patented Jan. 24, 1967 of an embodiment such as shown in FIG. 16 in a specific form of mounting,

FIG. 20 is an end elevational view of a second form of brush component,

FIG. 21 is a transverse sectional view taken on the line 2121 of FIG. 20 and FIG. 22 is a flat development view of the contact or brush element of the device shown in FIGS. 20 and 21.

Referring first to FIGS. 1-10, FIG. 1 shows in what is probably an average actual size for the illustrated embodiment of the invention while FIGS. 2-9 show details in sufficiently large scale to be'illustrated and understood. The base 1 is of cylindrical configuration and is formed of a suitable non-conductive material, e.g., ceramic or plastic, and at one side thereof is provided with a coaxially disposed smaller diameter shank portion 2 adapted to closely fit an opening in a panel P, said shank being secured therein by any appropriate means as, for example, a snap ring 3 engaging a groove 4 in the portion of the shank which projects beyond the panel P.

Projecting from the shank in the axial line thereof is an elongated cylindrical core element 5 of lesser diameter than said shank and which terminates in a head 6 of larger diameter than the core element and wound about the core is what will be referred to as the resistance assembly here comprising a plurality of resistance wires 7, 8 and 9 laid side by side in physical contact with each other and wound in a helix covering the entire surface of the core and, in effect, forming a triple thread thereon. The shank 2 and head 6 thus serve to hold the convolutions of the resistance assembly from movement along the core. The wires extend through holes in the head 5 and are either provided with solder bead heads 10 to secure them or they may be simply twisted together. These wires at the base are soldered one each to a plurality of conductors 11, 12 and 13 extending through the base and projecting beyond the end of the base as socket engaging pin elements. Alternatively, the head may be provided with sockets in place of the pins or with other means presently to be described. These wires are provided with a nonconductive coating to prevent shorting between the adjacent convolutions thereof and this coating is removed from the outermost surface for contact by the novel brush element now to be described. Thus the outer surface of the resistance component is, for all practical purposes, a wholly conductive surface.

The brush element or component comprises a ring 14 of non-conductive material having inwardly extending side flanges 15, 15 which are only slightly larger than the outer diameter of the resistance assembly comprising the core and the wires 7, 8 and 9 wound thereon and said flanges combined with the inner surface of the ring to define a toroidal space within the ring. As here shown, the brush is formed of identical semicircular halves cemented together.

Housed within the said toroidal space is a brush member 16 comprising a short closely wound spring of slightly oval configuration in end elevation, the minor diameter of which is only slightly less than the outer diameter of the resistance assembly to afford yielding contact therewith and the outer major diameter of this brush spring being greater than the minor diameter of the flanges 15, 15, wherefore the brush is retained within the ring. Additionally, the ends 17, 17 of the spring may engage appropriate recesses formed in the inner surface of the ring to assure that as the ring is rotated, the spring comprising the brush will rotate with it.

The wire from which the spring 16 is wound is, of course, resilient and conductive and preferably is of substantially the same diameter as the diameter of the wires 7, 8 and 9. Because of the yielding point contact achieved by the oval configuration of the spring 16 it is obvious that as the brush component is rotated the convolutions of the spring 16 will follow the helix of the wires 7, 8 and 9 constituting the resistance assembly and form an electrical interconnection or short between those wires. FIG. shows a representative circuit in which a unit 18 is connected to the device and adjustment of the device is employed to vary the current supply to a controlled unit 19. The wires 7 and 8 are connected in series by the brush at a desired resistance creating point in the length thereof which simultaneously connects them to the wire 9 which is connected to the unit 19, wherefore, the device acts as an adjustable potentiometer since as the brush component moves toward the head 18 the resistance increases and vice versa. Alternatively, while it is not shown in the drawings, it will be appreciated from an inspection of FIG. 10 that the coil represented by the numeral 9 might be reversely connected and might have a greater or lesser resistance than the combined resistance of the wires 7 and 8 wherefore, movement of the brush outwardly from the base will be increasing the resistance of the wires 7 and 8 but decreasing the resistance of the wire 9 wherefore, because of such differential, a very fine adjustment of resistance may be achieved. This is pointed out as another possible use of the illustrated device in which the novel character sought tobe protected is not the manner in which the conductor elements happen to be connected in a circuit but rather relates to the novel means of adjustment and the compact construction which incidentally, permits the device to be made in extremely small dimensions. Also, while the device is shown here as having three wires Wound on the core element to permit it to be used as a potentiometer, it will also be obvious that if only two of the wires are connected to a source of energy in a circuit, the device will act as a variable resistance in a series circuit.

Heretofore the discussion has been of the adjustment and variation of current achieved by rotating the brush component with resultant movement thereof axially of the resistance assembly by reason of the engagement with the helically disposed wires thereon. The yielding engagement of the spring 16 with the wires 7, 8 and 9 also permits the brush component to be moved manually bodily without rotation along the resistance assembly for a coarse adjustment of the device, the head 6 and shank 2 holding the Wires 7, 8 and 9 against movement along the core 5, leaving the rotative movement above described for the fine adjustment.

FIG. 9 shows an alternative form of brush spring 20 which may be used in the ring 14, said brush spring being wound considerably larger than the diameter of the resistance assembly but no larger than the inner diameter of the brush component housing ring and having the convolutions thereof inwardly indented at two or more points as at 21 to provide coil engaging points yieldingly engaging the resistance assembly wires. This spring will engage the convolutions of the resistance assembly wires and will move axially therealong in response to rotative movement and also permits the bodily axial movement for coarse adjustment of the brush component.

FIGS. 11 and 12 shows a similar device adapted for mounting on a printed circuit board B at the circuit carrying side thereof. As shown, the base 22 has a shank 23 projecting through an opening in the board from the circuit carrying side thereof said shank being secured by a snap ring 24 engaging a groove 24' in the projecting portion of the shank. The face of the base opposite the face from which the shank projects carries a resistance assembly comprising a core element 25 upon which resistance wires 26, 27 and 28 corresponding to the wires 7, 8 and 9 are wound in the same manner. A rotatable brush element 29 is rotatable and slidable thereon and said brush element may be either of the forms previously described or may have any other suitable contact means that may partake of bodily axial movement or rotative adjustment movement as desired. The face of the base from which the resistance assembly projects carries three metal terminal pins 30, 31 and 32 to which the resistance wires 26, 27 and 28 are connected and to which leads 33, 34 and 35 extending from conductors on the board B are also connected. The mode of operation is the same as in the first embodimentaxial, non-rotative movement of the brush providing a coarse adjustment while rotative movement of the brush produces slow axial movement and consequent fine adjustment of the current flowing through the Wires 26, 27 and 28 as they may be shorted by the brush. Again it is to be emphasized that the invention is not to be deemed to derive in the manner in which this resistance device happens to be connected in any particular circuit but in the novel resistance and brush components which permit structure of very small size and permit both a coarse and a fine adjustment to be made without having separate instrumentalities therefor. In other words, this device can replace both a main variable resistance and a trimming resistance means or a main potentiometer and a trimming potentiometer.

FIGS. 13, 14, 14a and 15 show a modification in which the adjustment means is disposed at the opposite side of a board B. In this form, the base 36 is provided with a shank 37 which extends through and is secured in an opening in the board B by any appropriate means and conductors 38, 39 and 40 similar to pins 11, 12 and 13 extend through the base and shank for connection by appropriate leads to conductor elements on the surface of the board.

A resistance assembly comprising a supporting core 41 projects axially from the opposite side of the base including resistance wires 42, 43 and 44 helically wound thereon as in the previously described embodiment. An axially rotatably and bodily movable bmsh component 45 is mounted on the resistance assembly which may be of the type shown in FIGS. 13 and 14 except that the outer surface of the brush body is provided with diametrically opposite grooves 47, 47 extending parallel to the axial line of the brush, said grooves being loosely engaged by inwardly extending complementary rib portions 48, 48 on the exterior of a cap 49 which houses the resistance assembly and which has a split open end 50 detachably engageable with a peripheral groove 51 on the side surface of the base. Thus by rotating the cap, the brush is rota-ted and through engagement with the brush thereof with the helically wound resistance wires is caused to partake of axial movement along the resistance assembly, the frictional grip of the split end 50 of the cap serving to prevent unintended rotation of the brush. Alternatively, as shown in FIG. 14a the cap 49' may be formed without interengagement with the brush and thus serve only to prevent movement of the brush without first removing the cap.

FIG. 16 shows an elongated resistance assembly comprising a cylindrical core 52 upon which a plurality of resistance wires generally indicated at 53 are helically Wound and a rotatable and axially bodily displaceable brush component 54 is mounted thereon for movement in either of the methods above referred to. This form of the device is intended for those uses in which the principle of adjustment of the invention is desired to be incorporated in some particular holding means other than those above illustrated. By way of example, a resistance element of the type shown in FIG. 16 may be mounted in a supporting bracket 55 formed of bent wire as shown in FIGS. 17, 18 and 19, the opposite ends of the resistance element being secured adhesively within bushings 56, 56 and the entire unit then being mounted in the supporting bracket, it being obvious that one or the other of the bushings 56 will be adhesively secured to the exterior surface of the resistance component as an incident to assembly.

FIGS. 20, 21 and 22 illustrate a brush component 57 which may be used in place of either of the brush elements previously discussed said brush element comprising a torus 58 formed of non-conductive material and having radially extending opposite slots 59, 59 at the opposite side faces. The brush component 60 comprises a sheet of metal adapted to be rolled into almost a complete circle and to fit loosely within the central axial bore 61 of the brush component 58. One of the ends of the inner face of the brush component is provided with an embossed series of grooves 62 corresponding to the diameter and pitch of the threads forming the outer surface of the resistance assembly on which the brush component is to be used. The inner diameter of this brush component is, of course, only slightly less than the outer diameter of the resistance assembly wherefore the slight distortion imparted thereto by being mounted on the resistance assembly affords good electrical contact. The brush component on the sides thereof is further provided with laterally extending tab elements 63 which are bent outwardly and loosely engage the recesses 59 to cause the brush component 60 to rotate with the base 58 Without adversely affecting the resilient engagement of the brush component with the resistance assembly. It will be understood that wherever desirable, a brush component assembly of this character may be employed in place of any of the others heretofore described so long as it achieves the function of being capable of bodily axial movement without rotation and of axial movement upon rotation by reason of the thread-like engagement with the wires constituting the resistance assembly.

One characteristic of all forms of the invention is the fact that by close winding the resistance assembly and securing the convolutions thereof against movement longitudinally of the core, the necessity for the use of threadlike grooves to retain the wires and for spacing the Wires from each other is eliminated. The result is that for any given length of core element, a greater length of resistance Wire can be employed or, conversely, a given length of resistance Wire can be accommodated in a shorter length of core. Both of these considerations are of greatimportance in the design of miniature and subminiature resistance components.

While the foregoing specification has disclosed, by way of example, certain presently preferred embodiments of the invention, the invention is not to be deemed to be limited to the precise details of construction thus disclosed as will be evidenced by the discussion at various points in the specification of the fact that certain obvious substitutions and modifications can be made. Accordingly, the invention is not to be deemed to be limited to such details of disclosure and it will be understood that the invention includes as Well all such changes and modifications in the parts and in the construction combination and arrangement of parts as shall come within the purview of the appended claims.

I claim:

1. In a variable resistance device, a base, a resistance component carried by said base and comprising a plurality of electrical conductors and an elongated rigid supporting member of circular cross section, said conductors being disposed in side-by-side physically contacting relation in helically wound configuration upon a cylindrical surface of said supporting member with resultant formation of a cylindrical surface of said resisttime component which is electrically conductive, means at opposite ends of the portion of said supporting member on which said conductors are wound operative to prevent movement of the conductors axially of said portion, said conductors having such cross sectional configuration that the outer surfaces of adjacent convolutions form a helical groove on the cylindrical surface of said resistance component for-med by said conductors, the surfaces of said conductors in con-tact with each other and with said supporting member being electrically nonconductive, and the surface portions of said conductors which are remote from the surface of the support being electrically conductive, terminal means carried by said base affording separate connection of said conductors in an electrical circuit, and an electrically conductive brush component resiliently contacting the exterior surface of said resistance component, said brush component comprising a non-conductive ring surrounding and carrying a brush element comprising a metal spring of substantially oval configuration having a minor diameter slightly less than the outer diameter of said helically wound conductors and a major diameter sufficiently greater than said minor diameter to permit said spring to be expanded in the direction of said minor diameter to accommodate said helically wound conductors without causing said spring to be so shortened along said major diameter as to cause said spring to engage said helically wound conductors at the portions represented by said major diameter whereby relative rotation between said brush component and said conductors will effect relative movement between the brush component and said conductors axially of the helix formed by said conductors with resultant variation in the resistance imposed on a current passing through said conductors and said brush component.

2. A variable resistance device as claimed in claim 1 in which the brush element comprises a spring of greater diameter than said helically wound conductors and having the coils thereof indented at spaced points thereon in the direction of the axial line of the spring for yielding engagement with the uninsulated portions of said helically wound conductors.

3. In a variable resistance device, a resistance component comprising a plurality of elongated electrical conductors and an elongated rigid supporting member of circular cross section; said conductors being disposed in side-by-side physically contacting relation in helically wound configuration upon a cylindrical surface of said rigid supporting member for said conductors, means at opposite ends of said cylindrical supporting member restraining said conductors against movement thereon axially of said supporting member, said conductors having such cross sectional configuration that the outer surfaces of adjacent convolutions form at least one helical groove on the surface of said resistance component created by said conductors, separate terminal means connected one each to each of said conductors and affording means of connection of each of said conductors separately to components of an electrical circuit, means insulating said conductors from one another and the surfaces of said conductors which contact each other and said supporting member being electrically non-conductive, and the surfaces of said conductors remote from the surface of said supporting member being electrically conductive, and a brush component comprising a non-conductive ring surrounding and carrying a brush element comprising a metal spring of oval configuration having a minor diameter slightly less than the outer diameter of said helically wound conductors and a major diameter sufficiently greater than said minor diameters to permit said spring to 'be expanded in the direction of said minor diameter to accommodate said helically wound conductors without causing said spring to be so shortened along said major diameter as to cause said spring to engage said helically Wound conductors at the portions represented by said major diameter and being movable optionally both back and forth on said conductive surfaces of said conductors in directions parallel to the axial line of the surface on which said conductors are supported, and said resistance component and said brush component being relatively rotatable about the axial line of said resistance at all positions thereof to which said brush component may be moved; said conductive element of said brush component serving to electrically interconnect said conductors at varying distances from said terminals with resultant variation in the electrical resistance between said terminals and the points of shorting between said conductors effected by said brush component, whereby relative rotation between said brush and said resistance component effects axial movement of said brush.

4. A variable resistance device as claimed in claim 3 in which said brush element comprises a metal spring of greater diameter than said helically wound conductors and having the coils thereof indented at spaced points thereon in the direction of the axial line of the spring for yielding engagement with the electrically conductive portions of said helically wound conductors.

5. In a variable resistance device, a base, a resistance component carried by said base and comprising at least three electrical conductors and an elongated rigid supporting member of circular cross section, said conductors being disposed in side-by-side physically contacting relation in helically wound configuration upon a cylindrical surface of said supporting member with resultant formation of a cylindrical surface of said resistance component which is electrically conductive, means at opposite ends of the portion of said supporting member on which said conductors are wound operative to prevent movement of the conductors axially of said portion and to constitute anchoring means for the free ends of said conductors, said conductors having such cross sectional configuration that the outer surfaces of adjacent convolutions form a helical groove on the cylindrical surface of said resistance component formed by said conductors, the surfaces of said conductors in contact with each other and with said supporting member being electrically nonconductive, and the surface portions of said conductors which are remote from the surface of the support being electrically conductive, terminal means carried by said base affording separate connections extending axially away from said conductors, and an electrically conductive brush component resiliently contacting the exterior surface of said resistance component formed by helically wound conductors and engaging said conductive surfaces of adjacent conductors to efiect electrically conductive connection therebetween and including means engaging at least one of the grooves formed by adjacent conductors whereby relative rotation between said brush component and said conductors will effect relative movement between the brush component and said conductors axially of the helix formed by said conductors with resultant variation in the resistance imposed on a current passing through said conductors and said brush component.

6. A variable resistance device as claimed in claim 5 in which said resilient contact between said brush component and said resistance component permits bodily non-rotative movement of said brush component along said resistance component parallel to the axial line of said resistance component; said means at the opposite ends of said supporting member serving to prevent movement of the convolutions of said conductors under the influence of said non-rotative movement of said brush component.

7. A variable resistance device as claimed in claim 5 in which two of the conductors are connected in series relation in an electrical circuit while the third of said conductors constitutes a variable tap connected to said two of said conductors for variable diversion of a portion of the current passing through said two conductors.

8. A variable resistance electrical device as claimed in claim 5 in which said brush component comprises a non-conductive ring surrounding and carrying a brush element comprising a metal spring of oval configuration having a minor diameter slightly less than the outer diameter of said helically wound conductors and a major diameter sufficiently greater than said minor diameter to permit said spring to be expanded in the direction of said minor diameter to accommodate said helically wound conductors without causing said spring to be so shortened along said major diameter as to cause said spring to engage said helically wound conductors at the portions represented by said major diameter.

9. A variable resistance device as claimed in claim 5 in which said brush component comprises a non-conductive ring surrounding and carrying a brush element comprising a metal spring of greater diameter than said helically wound conductors and having the coils thereof indented at spaced points thereon in the direction of the axial line of the spring for yielding engagement with the uninsulated portions of said helically wound conductors.

References Cited by the Examiner UNITED STATES PATENTS 432,894 7/1890 Parrish 338176 1,276,384 8/1918 Lundy 33897 1,491,345 4/1924 Gargan 338--126 X 1,561,137 11/1925 Burns 338143 1,589,501 6/1926 Wohl 338145 1,620,573 3/1927 Rostron 338143 2,204,623 6/1940 Ruben 338-161 2,548,591 4/1951 Crowley 338-426 2,724,034 11/1955 Altieri 338-126 2,849,350 8/1958 Roach 338-161 X 3,044,033 7/1962 Mucher 338-163 ANTHONY BARTIS, Primary Examiner.

RICHARD M. WOOD, Examiner.

R. F. STAUBLY, Assistant Examiner. 

1. IN A VARIABLE RESISTANCE DEVICE, A BASE, A RESISTANCE COMPONENT CARRIED BY SAID BASE AND COMPRISING A PLURALITY OF ELECTRICAL CONDUCTORS AND AN ELONGATED RIGID SUPPORTING MEMBER OF CIRCULAR CROSS SECTION, SAID CONDUCTORS BEING DISPOSED IN SIDE-BY-SIDE PHYSICALLY CONTACTING RELATION IN HELICALLY WOUND CONFIGURATION UPON A CYLINDRICAL SURFACE OF SAID SUPPORTING MEMBER WITH RESULTANT FORMATION OF A CYLINDRICAL SURFACE OF SAID RESISTANCE COMPONENT WHICH IS ELECTRICALLY CONDUCTIVE, MEANS AT OPPOSITE ENDS OF THE PORTION OF SAID SUPPORTING MEMBER ON WHICH SAID CONDUCTORS ARE WOUND OPERATIVE TO PREVENT MOVEMENT OF THE CONDUCTORS AXIALLY OF SAID PORTION, SAID CONDUCTORS HAVING SUCH CROSS SECTIONAL CONFIGURATION THAT THE OUTER SURFACES OF ADJACENT CONVOLUTIONS FORM A HELICAL GROOVE ON THE CYLINDRICAL SURFACE OF SAID RESISTANCE COMPONENT FORMED BY SID CONDUCTORS, THE SURFACES OF SAID CONDUCTORS IN CONTACT WITH EACH OTHER AND WITH SAID SUPPORTING MEMBER BEING ELECTRICALLY NONCONDUCTIVE, AND THE SURFACE PORTIONS OF SAID CONDUCTORS WHICH ARE REMOTE FROM THE SURFACE OF THE SUPPORT BEING ELECTRICALLY CONDUCTIVE, TERMINAL MEANS CARRIED BY SAID BASE AFFORDING SEPARATE CONNECTION OF SAID CONDUCTORS IN AN ELECTRICAL CIRCUIT, AND AN ELECTRICALLY CONDUCTIVE BRUSH COMPONENT RESILIENTLY CONTACTING THE EXTERIOR SURFACE OF SAID RESISTANCE COMPONENT, SAID BRUSH COMPONENT COMPRISING A NON-CONDUCTIVE RING SURROUNDING AND CARRYING A BRUSH ELEMENT COMPRISING A METAL SPRING OF SUBSTANTIALLY OVAL CONFIGURATION HAVING A MINOR DIAMETER SLIGHTLY LESS THAN THE OUTER DIAMETER OF SAID HELICALLY WOUND CONDUCTORS AND A MAJOR DIAMETER SUFFICIENTLY GREATER THAN SAID MINOR DIAMETER TO PERMIT SAID SPRING TO BE EXPANDED IN THE DIRECTION OF SAID MINOR DIAMETER TO ACCOMMODATE SAID HELICALLY WOUND CONDUCTORS WITHOUT CAUSING SAID SPRING TO BE SO SHORTENED ALONG SAID MAJOR DIAMETER AS TO CAUSE SAID SPRING TO ENGAGE SAID HELICALLY WOUND CONDUCTORS AT THE PORTIONS REPRESENTED BY SAID MAJOR DIAMETER WHEREBY RELATIVE ROTATION BETWEEN SAID BRUSH COMPONENT AND SAID CONDUCTORS WILL EFFECT RELATIVE MOVEMENT BETWEEN THE BRUSH COMPONENT AND SAID CONDUCTORS AXIALLY OF THE HELIX FORMED BY SAID CONDUCTORS WITH RESULTANT VARIATION IN THE RESISTANCE IMPOSED ON A CURRENT PASSING THROUGH SAID CONDUCTORS AND SAID BRUSH COMPONENT. 